The present invention relates to a new process for producing impregnated silica and to the use of the resultant impregnated silica, particularly in analytical methods and liquid or gas phase chromatography and for the purification of industrial products.
Since a few years, substantial improvements have been made in analytical liquid chromatography through the use of adsorbents consisting of silica microparticles. The latter, when used in the presence of water in controlled amount, are very efficient as concerns certain separations. They are not, however, satisfactory for other separations. It has then been attempted to modify these silica microparticles by depositing polar compounds thereupon, hereinafter designated as "solvents", in order to improve the selectivity as concerns certain types of separations, for example, those for which said polar compounds have a substantial selectivity when used in conventional liquid-liquid or liquid-vapor extraction.
Unfortunately it has been found that, when this deposition of "solvent" is effected according to conventional techniques, silica loses a large part of its efficiency; when expressing the latter as the "equivalent height of a theoretical plate" (EHTP), ratios of 10:1 are commonly noted when comparing the unimpregnated silicas to the impregnated silicas, and the so-prepared columns are not stable.